1. Field of the Invention
The present invention relates to a manufacturing method for an ink jet printer head of an on-demand type such that ink droplets are discharged by utilizing deformation of a piezoelectric member and, more particularly, to such a manufacturing method characterized in pretreatment for formation of electrodes and wiring patterns thereof for applying electric power to the piezoelectric member.
2. Description of the Prior Art
Conventionally known are various ink jet printer heads of a so-called on-demand type such that ink droplets are discharged in accordance with a print command. A known example of such ink jet printer heads is one designed to discharge ink droplets by utilizing deformation of a piezoelectric member upon application of electric power thereto. Such an ink jet printer head is disclosed in Japanese Patent Laid-open No. Hei 4-363250 (corresponding to U.S. Pat. No. 5,311,218), Japanese Patent Laid-open No. Hei 5-96727 (corresponding to U.S. Pat. No. 5,311,219), and Japanese Patent Laid-open No. Hei 5-269994 (corresponding to U.S. Pat. No. 5,301,404), for example. The structure of the ink jet printer head disclosed in Japanese Patent Laid-open Nos. Hei 5-96727 and Hei 5-269994 will now be described with reference to FIGS. 9(A) to 11(C) showing the sequence of steps of manufacturing the ink jet printer head.
As shown in FIG. 9(A), a substrate 4 having a three-layer structure consisting of a bottom plate 1, a lower layer 2, and a piezoelectric member 3 is formed in the first step. The bottom plate 1 is formed of a highly rigid and less thermally deformable material such as ceramics or glass. The lower layer 2 is formed by applying an adhesive primarily composed of an epoxy resin to the upper surface of the bottom plate 1 to form an adhesive layer having a given thickness, and then curing the adhesive layer. The piezoelectric member 3 is bonded to the lower layer 2 in such a manner that the direction of polarization of the piezoelectric member 3 accords with the direction of thickness of the piezoelectric member 3. In forming the lower layer 2, the thickness thereof is adjusted by grinding the adhesive layer after curing it.
As shown in FIG. 9(B), the substrate 4 is next cut to form a plurality of parallel channels 5 at given intervals, each channel 5 having a depth ranging from the upper surface of the piezoelectric member 3 to the interior of the lower layer 2. By this cutting work of the substrate 4, a plurality of side walls 6 are simultaneously formed so that adjacent ones of them are located on the opposite sides of each channel 5. Each side wall 6 consists of an upper side wall 6(A) formed from the piezoelectric member 3 and a lower side wall 6(B) formed from the lower layer 2.
Next, the substrate 4 is subjected to electroless plating for forming electrodes 7 and wiring patterns 8 (see FIG. 11(A)). As a pretreatment for the electroless plating, a catalyzing/accelerating process is performed. The catalyzing process is performed by immersing the substrate 4 into a catalyst liquid containing palladium chloride (PdCl.sub.2), stannous chloride (SnCl.sub.2), and concentrated hydrochloric acid (HCl) to adsorb a complex compound of Pd and Sn on the inner surfaces of the channels 5 and the upper surface of the piezoelectric member 3. The accelerating process is performed to convert the complex compound adsorbed by the catalyzing process into a catalyst. By this process, the complex compound is converted into metallized Pd as a catalyst core.
As shown in FIG. 9(C), a dry film 9 is next attached to the upper surface of the piezoelectric member 3. Then, as shown in FIG. 10(A), a resist mask 10 is placed on the dry film 9 to perform exposure and development. As a result, as shown in FIG. 10(B), a pattern resist film 11 is formed on the upper surface of the piezoelectric member 3 from the dry film 9 so as to cover channel inside surfaces 7a as electrode forming portions on which the electrodes 7 are to be formed later and wiring pattern forming portions 8a on which the wiring patterns 8 are to be formed later. At this time, the metallized Pd is exposed to the channel inside surfaces 7a and the wiring pattern forming portions 8a, and the other Pd adsorbed on the upper surface of the piezoelectric member 3 is covered with the pattern resist film 11.
Next, the substrate 4 on which the pattern resist film 11 has been formed is immersed into a plating liquid to perform electroless plating. The plating liquid to be used is a low-temperature plating liquid containing nickel and phosphorus. When the substrate 4 on which the pattern resist film 11 has been formed is immersed into the plating liquid, the metallized Pd in the exposed condition acts as a catalyst core to deposit plating on the channel inside surfaces 7a and the wiring pattern forming portions 8a. As a result, the electrodes 7 are formed on the channel inside surfaces 7a, and the wiring patterns 8 are formed on the wiring pattern forming portions 8a as shown in FIG. 11(A). Then, as shown in FIG. 11(B), the pattern resist film 11 is separated to thereby finish the electroless plating.
Next, as shown in FIG. 11(C), a top plate 12 is bonded to the substrate 4 so as to cover the upper openings of the channels 5, and a nozzle plate 14 having a plurality of ink discharge openings 13 respectively communicating with the front openings of the channels 5 is then bonded to the substrate 4 and the top plate 12 so as to cover the front openings of the channels 5. Further, an ink supply pipe 15 for supplying ink to the channels 5 is mounted to the top plate 12, thereby completing an ink jet printer head 16. Thus, the channels 5 are surrounded by the top plate 12 and the nozzle plate 14 to thereby form a plurality of ink chambers. In bonding the nozzle plate 14, the front end surfaces of the substrate 4 and the top plate 12 are cut to be made flush.
In manufacturing the ink jet printer head 16 disclosed in Japanese Patent Laid-open Nos. Hei 5-96727 and Hei 5-269994, the electrodes 7 and the wiring patterns 8 are formed by the above-mentioned steps, in which the electrodes 7 having no pinholes can be formed on the channel inside surfaces 7a. However, the prior art ink jet printer head 16 has the following problems.
The first problem will now be described. In immersing the substrate 4 on which the pattern resist film 11 has been immersed into the plating liquid, so as to form the electrodes 7 and the wiring patterns 8 by electroless plating, there is a case where the pattern resist film 11 is swelled by the plating liquid, and in particular, portions of the pattern resist film 11 covering the upper end surfaces of the side walls 6 are floated or separated by the plating liquid. If the pattern resist film 11 is thus floated or separated from the upper end surfaces of the side walls 6, the Pd covered with the pattern resist film 11 is exposed to act as a catalyst core for electroless plating, thereby depositing plating on the upper end surfaces of the side walls 6. As a result, the adjacent electrodes 7 formed on the channel inside surfaces 7a are short-circuited in some case. This defect is due to the following reason. In attaching the dry film 9 to the upper surface of the piezoelectric member 3 with good adhesion, it is desired to enough harden the dry film 9 at a baking temperature of 150.degree. C. or higher. To the contrary, when the piezoelectric member 3 polarized is heated to 130.degree. C. or higher, deterioration of polarization in the piezoelectric member 3 occurs. Accordingly, the baking temperature must be suppressed to about 130.degree. C. As a result, the pattern resist film 11 is not enough hardened because of the low baking temperature of about 130.degree. C., causing ready swelling of the pattern resist film 11 immersed into the plating liquid.
The second problem will next be described. Just before depositing the plating by electroless plating, a hydrophilic process for the substrate 4 is usually performed with an ethanol liquid or an activating agent to improve the deposition of the plating on the channel inside surfaces 7a. Although not described in the prior art shown in FIGS. 9(A) to 11(C), the hydrophilic process activates the surface of the pattern resist film 11. However, when the hydrophilic process is performed, there is a case where the Pd adsorbed on the channel inside surfaces 7a and the wiring pattern forming portions 8a is partially separated and the Pd thus separated is partially deposited to the activated surface of the pattern resist film 11. As a result, when the substrate 4 in this condition is immersed into the plating liquid to deposit the plating, the plating is undesirably deposited also to the surface of the pattern resist film 11 on which the plating must not be deposited, so that the plating deposited on the surface of the pattern resist film 11 continues to the electrodes 7 and the wiring patterns 8. Accordingly, in separating the pattern resist film 11, the electrodes 7 and the wiring patterns 8 are partially pulled to be separated in some case.
The third problem will now be described. While the resist mask 10 is placed on the dry film 9 attached to the upper surface of the piezoelectric member 3, and exposure and development are performed with respect to the dry film 9 to thereby form the pattern resist film 11, it is difficult to accurately form a pattern of the pattern resist film 11 into a desired shape. That is, the pattern resist film 11 is formed by placing the resist mask 10 having a predetermined pattern on the dry film 9, and next directing light for the exposure onto the dry film 9 through the resist mask 10. However, since the upper surface of the piezoelectric member 3 on which the dry film 9 is attached has microscopic asperities, there occurs irregular reflection of the exposure light on the microscopic asperities. The exposure light thus irregularly reflected undesirably sensitizes a portion of the dry film 9 masked by the resist mask 10. Accordingly, the width of the pattern of the pattern resist film 11 becomes different from the width of the pattern described in the resist mask 10. Further, an edge portion of the pattern resist film 11 becomes remarkably dull.
While the third problem may be solved by mirror-finishing the upper surface of the piezoelectric member 3 to remove the asperities, this work is costly and therefore unpractical.